1. Field of the Invention
The present invention relates in general to the field of circuit interrupters. More particularly, the present invention relates to a ground fault circuit interrupter on the line side of a main electrical panel, which is before the point at which the neutral of the power supply is connected to the system grounding conductor (commonly known as the bonding point). The bonding point for utility power is typically accomplished at the main electrical panel, also known as the service entrance panel. This panel ma be used in conjunction with a transfer switch or power inlet for use with an auxiliary power supply such as a portable generator. In particular, such a device would be useful when powering a structure from an unbonded power supply such as utility power supply or a floating-neutral portable generator.
2. Discussion of the Related Art
Ground fault circuit interrupters (GFCI) are commonly used in a number of applications where there is potential for current to flow outside of a load. All known current ground fault protection is located on the load side, meaning that it is located downstream from the bonding point, between the main electrical panel and the user. For example, it is very common for outlets or switches to contain GFCI devices within the receptacle. This means that the current flows from an external source first to the main electrical panel, and flows next to the GFCI receptacle. The GFCI receptacle provides a single, hot supply of current. When properly functioning, there is a single return supply of current that flows through the receptacle. However, in certain dangerous scenarios, at least a portion of the current is routed outside the device that is plugged into the outlet, which creates two current returns: one through the outlet and one outside the outlet. When this occurs, the GFCI is immediately actuated to cut off the hot supply of current such that the electrical circuit is broken. These types of GFCI outlets disconnect the power supply in the event that excessive current flows to the ground. One common application for these types of outlets is in settings where there is frequent water use.
A typical GFCI device measures the amount of current flowing from the outlet in comparison with current returning to the outlet. In the event that there is less flow returning (meaning some of that current is flowing through another source to the ground), the hot source is stopped, which prevents further flow of current outside of the circuit. This is an effective means to prevent potentially dangerous situations because the hot source is the only supply of current, and ending such flow will break the electrical circuit.
However, this configuration is ineffective where a diversion of power occurs upstream of the main electrical panel. When properly functioning, there is a single return of current from the main electrical panel to the power supply; however, in the event of a diversion in current upstream of the main electrical panel, there are two current paths: one through the wiring to the main electrical panel and one through the diversion to the ground. The traditional load-side GFCI configuration that cuts off the power supply is ineffective on an upstream, line side of the circuit because shutting off the hot supply after the point of diversion does not break the circuit. Rather it would supply the entire flow of current through the diversion. A configuration in which this situation may occur is when an external power supply, such as a portable generator, is present and an individual accidentally interferes with the current flow between the power supply and the main electrical panel.
What is needed, therefore, is a current interrupter device that may be installed between the power supply and the main electrical panel such that current flow may be stopped when a diversion upstream of the main electrical panel occurs, such as when an individual accidentally interferes with the supply of power prior to the point at which power is supplied to the main electrical panel.